For years there have been a multitude of attempts and ideas for providing a satisfactory seal when a rotatable shaft is angularly misaligned resulting in run out of the shaft. Typically the solutions presented have failed to provide an adequate seal while allowing for an acceptable amount of shaft misalignment during operation. The problem is especially acute in product seals where the potential for shaft to bore misalignment may be maximized. A typical solution in the prior art is to increase the operating clearance between the rotating shaft and sealing members to create a “loose” clearance or operating condition. “Loose” running for adjustment or response to operational conditions, especially misalignment of the shaft with respect to the stator or stationary member, however, typically reduces or lowers the efficiency and efficacy of sealing members.
Labyrinth seals, for example, have been in common use for many years for application to sealing rotatable shafts. A few of the advantages of labyrinth seals over contact seals are increased wear resistance, extended operating life and reduced power consumption during use. Labyrinth seals, however, also depend on a close and defined clearance with the rotatable shaft for proper function. Shaft misalignment is also a problem with “contact” seals because the contact between the seal and misaligned shaft typically results in greater wear. Abrasiveness of the product also affects the wear pattern and the useful life of the contact seals.
Prior attempts to use fluid pressure (either vapor or liquid) to seal both liquid and solid materials in combination with sealing members such as labyrinth seals or contact seals have not been entirely satisfactory because of the “tight” or low clearance necessary to create the required pressure differential between the seal and the product on the other side of the seal (i.e., the tighter the seal, the lower the volume of fluid required to maintain the seal against the external pressure of material.) Another weakness in the prior art is that many product seals expose the movable intermeshed sealing faces or surfaces of the product seal to the product resulting in aggressive wear and poor reliability. Furthermore, for certain applications, the product seal may need to be removed entirely from the shaft seal assembly for cleaning, because of product exposure to the sealing faces or surfaces.
The prior art then has failed to provide a solution that allows both a “tight” running clearance between the seal members and the stationary member for efficacious sealing and a “loose” running clearance for adjustment or response to operational conditions especially misalignment of the rotatable shaft with respect to the stator or stationary member.